Miocene acidic explosive volcanism in the Bukk Foreland, Hungary

Identifying eruptive sequences and searching for source locations

Alexandru Szakács, E. Márton, Teréz Póka, Tibor Zelenka, Z. Pécskay, Ioan Seghedi

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

Neogene volcanism began in the Hungarian part of the Carpatho-Pannonian area with explosive eruptions of large-volume acidic magmas during the Miocene. It was followed by andesitic volcanism which is partially coeval with the acidic one. Three main acidic tuff horizons are known, referred to as the Lower, Middle and Upper Rhyolitic Tuff, Eggenburgian/Ottnangian, Karpatian/Lower Badenian and Lower Sarmatian in age, respectively. Their onshore-deposited counterparts, found in the basin-rim regions such as the Bukk Foreland, are difficult to identify and correlate. Complex investigation, including lithostratigraphy, petrography, petrochemistry, K-Ar geochronology and paleomagnetic studies, were recently undertaken in the Bukk Foreland area. The three tuff complexes have been identified, distinguished and characterized. The Lower Tuff Complex (21.0-18.5 Ma, 80°to 90°counterclockwise rotation) is well exposed in the northern part of the area and consists of biotite-rich rhyolitic Plinian pumice fall deposits, welded and non-welded ignimbrites, phreatomagmatic sequences and reworked tuffs. The Middle Tuff Complex (17.5-16.0 Ma, ca. 30°counterclockwise rotation) is widespread in the southern part of the area, and is characterized by a two-component chemistry (rhyolitic and andesitic), presence of mixed scoria-pumice pyroclastics, and an abundance of pyroxene crystalloclasts. It consists of a sequence of welded and non-welded ignimbrites, phreatomagmatic deposits and reworked tuffs. Various degrees of mixing of rhyolitic and andesitic magma result in extremely heterogeneous compositions ranging from typically rhyolitic to andesitic. The youngest Upper Tuff Complex is present in few outcrops at the western and eastern peripheries of the Bukk Foreland, as thick non-welded rhyolitic ignimbrites. Compositionally it is hardly distinguishable from the Lower Tuff Complex, but K-Ar ages are much younger (14.5-13.5 Ma) and no rotation is present in its paleomagnetic record. Volcanic source areas of the pyroclastic material should be somewhere south of the area, buried beneath younger sediments. Thickness and maximum pumice and lithic clast sizes of the pumice fall deposits of the Lower Tuff Complex suggest a northeast-oriented dispersal axis; imbrication in non-welded ignimbrites suggest transport in the same direction, hence source location for the oldest tuffs is possibly somewhere south of Eger. An elliptic aeromagnetic anomaly zone, present in that region, is consistent with such a hypothesis. On the other hand, magnetic anisotropy directions measured in welded ignimbrites of the Middle Tuff Complex converge in a zone NE of Mezokovesd (south of Harsany), where a wide elliptic positive gravity anomaly is located and thick andesite lava was described in boreholes. Maximum size of obsidian fiamme in the welded ignimbrite, measured at Tibolddaroc, is consistent with the location of the inferred source caldera in the area.

Original languageEnglish
Pages (from-to)413-435
Number of pages23
JournalActa Geologica Hungarica
Volume41
Issue number4
Publication statusPublished - 1998

Fingerprint

explosive volcanism
tuff
Miocene
ignimbrite
pumice
volcanism
obsidian
Badenian
imbrication
magnetic anisotropy
lithostratigraphy
petrography
gravity anomaly
caldera
geochronology
andesite
lava
clast
pyroxene
Neogene

Keywords

  • Bukk Foreland
  • Correlation of Miocene tuff horizons
  • Ignimbrites
  • Lithostratigraphy
  • Volcanology

ASJC Scopus subject areas

  • Geology

Cite this

Miocene acidic explosive volcanism in the Bukk Foreland, Hungary : Identifying eruptive sequences and searching for source locations. / Szakács, Alexandru; Márton, E.; Póka, Teréz; Zelenka, Tibor; Pécskay, Z.; Seghedi, Ioan.

In: Acta Geologica Hungarica, Vol. 41, No. 4, 1998, p. 413-435.

Research output: Contribution to journalArticle

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T1 - Miocene acidic explosive volcanism in the Bukk Foreland, Hungary

T2 - Identifying eruptive sequences and searching for source locations

AU - Szakács, Alexandru

AU - Márton, E.

AU - Póka, Teréz

AU - Zelenka, Tibor

AU - Pécskay, Z.

AU - Seghedi, Ioan

PY - 1998

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N2 - Neogene volcanism began in the Hungarian part of the Carpatho-Pannonian area with explosive eruptions of large-volume acidic magmas during the Miocene. It was followed by andesitic volcanism which is partially coeval with the acidic one. Three main acidic tuff horizons are known, referred to as the Lower, Middle and Upper Rhyolitic Tuff, Eggenburgian/Ottnangian, Karpatian/Lower Badenian and Lower Sarmatian in age, respectively. Their onshore-deposited counterparts, found in the basin-rim regions such as the Bukk Foreland, are difficult to identify and correlate. Complex investigation, including lithostratigraphy, petrography, petrochemistry, K-Ar geochronology and paleomagnetic studies, were recently undertaken in the Bukk Foreland area. The three tuff complexes have been identified, distinguished and characterized. The Lower Tuff Complex (21.0-18.5 Ma, 80°to 90°counterclockwise rotation) is well exposed in the northern part of the area and consists of biotite-rich rhyolitic Plinian pumice fall deposits, welded and non-welded ignimbrites, phreatomagmatic sequences and reworked tuffs. The Middle Tuff Complex (17.5-16.0 Ma, ca. 30°counterclockwise rotation) is widespread in the southern part of the area, and is characterized by a two-component chemistry (rhyolitic and andesitic), presence of mixed scoria-pumice pyroclastics, and an abundance of pyroxene crystalloclasts. It consists of a sequence of welded and non-welded ignimbrites, phreatomagmatic deposits and reworked tuffs. Various degrees of mixing of rhyolitic and andesitic magma result in extremely heterogeneous compositions ranging from typically rhyolitic to andesitic. The youngest Upper Tuff Complex is present in few outcrops at the western and eastern peripheries of the Bukk Foreland, as thick non-welded rhyolitic ignimbrites. Compositionally it is hardly distinguishable from the Lower Tuff Complex, but K-Ar ages are much younger (14.5-13.5 Ma) and no rotation is present in its paleomagnetic record. Volcanic source areas of the pyroclastic material should be somewhere south of the area, buried beneath younger sediments. Thickness and maximum pumice and lithic clast sizes of the pumice fall deposits of the Lower Tuff Complex suggest a northeast-oriented dispersal axis; imbrication in non-welded ignimbrites suggest transport in the same direction, hence source location for the oldest tuffs is possibly somewhere south of Eger. An elliptic aeromagnetic anomaly zone, present in that region, is consistent with such a hypothesis. On the other hand, magnetic anisotropy directions measured in welded ignimbrites of the Middle Tuff Complex converge in a zone NE of Mezokovesd (south of Harsany), where a wide elliptic positive gravity anomaly is located and thick andesite lava was described in boreholes. Maximum size of obsidian fiamme in the welded ignimbrite, measured at Tibolddaroc, is consistent with the location of the inferred source caldera in the area.

AB - Neogene volcanism began in the Hungarian part of the Carpatho-Pannonian area with explosive eruptions of large-volume acidic magmas during the Miocene. It was followed by andesitic volcanism which is partially coeval with the acidic one. Three main acidic tuff horizons are known, referred to as the Lower, Middle and Upper Rhyolitic Tuff, Eggenburgian/Ottnangian, Karpatian/Lower Badenian and Lower Sarmatian in age, respectively. Their onshore-deposited counterparts, found in the basin-rim regions such as the Bukk Foreland, are difficult to identify and correlate. Complex investigation, including lithostratigraphy, petrography, petrochemistry, K-Ar geochronology and paleomagnetic studies, were recently undertaken in the Bukk Foreland area. The three tuff complexes have been identified, distinguished and characterized. The Lower Tuff Complex (21.0-18.5 Ma, 80°to 90°counterclockwise rotation) is well exposed in the northern part of the area and consists of biotite-rich rhyolitic Plinian pumice fall deposits, welded and non-welded ignimbrites, phreatomagmatic sequences and reworked tuffs. The Middle Tuff Complex (17.5-16.0 Ma, ca. 30°counterclockwise rotation) is widespread in the southern part of the area, and is characterized by a two-component chemistry (rhyolitic and andesitic), presence of mixed scoria-pumice pyroclastics, and an abundance of pyroxene crystalloclasts. It consists of a sequence of welded and non-welded ignimbrites, phreatomagmatic deposits and reworked tuffs. Various degrees of mixing of rhyolitic and andesitic magma result in extremely heterogeneous compositions ranging from typically rhyolitic to andesitic. The youngest Upper Tuff Complex is present in few outcrops at the western and eastern peripheries of the Bukk Foreland, as thick non-welded rhyolitic ignimbrites. Compositionally it is hardly distinguishable from the Lower Tuff Complex, but K-Ar ages are much younger (14.5-13.5 Ma) and no rotation is present in its paleomagnetic record. Volcanic source areas of the pyroclastic material should be somewhere south of the area, buried beneath younger sediments. Thickness and maximum pumice and lithic clast sizes of the pumice fall deposits of the Lower Tuff Complex suggest a northeast-oriented dispersal axis; imbrication in non-welded ignimbrites suggest transport in the same direction, hence source location for the oldest tuffs is possibly somewhere south of Eger. An elliptic aeromagnetic anomaly zone, present in that region, is consistent with such a hypothesis. On the other hand, magnetic anisotropy directions measured in welded ignimbrites of the Middle Tuff Complex converge in a zone NE of Mezokovesd (south of Harsany), where a wide elliptic positive gravity anomaly is located and thick andesite lava was described in boreholes. Maximum size of obsidian fiamme in the welded ignimbrite, measured at Tibolddaroc, is consistent with the location of the inferred source caldera in the area.

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KW - Correlation of Miocene tuff horizons

KW - Ignimbrites

KW - Lithostratigraphy

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